Microbial Physiology notes lec20 11-12-10

Microbial Physiology notes lec20 11-12-10 - Microbial...

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Microbial Physio Lecture 20: Chemical Machines in Biology continued November 12, 2010 1. Exosomes: a. Fxn: Organelles of RNA degradation b. In bacteria( prokaryotes) its called the degradosome c. In eukaryotes it is called the exosome d. The exosome/degradosome all consists of long RNAse i. The RNAse in E.coli is called RNAseE ii. It consists of a long N terminal domain which is the active site its an RNase, so it hydrolyzes RNA iii. It has a long C terminal tail that is partially folded large denatured segment 1061 amino acids and the catalytic domain is about 300 amino acids and the rest of the protein is the partially unfolded domain of the exosome/degradasome that the enzymes of the exosome/degradosome are associated e. The exosome consist of at least 10 core proteins f. All possible 3’ to 5’ exoribonucleases are present this is the enzyme that is used to degrade RNA i. The exosomes fxn by different mechanisms and may be hydrolytic or phosphorolytic enzymes g. Exosome also has associated factors such as RNA helicases h. The primary fxn of the Exosomes/degradosome is to degrade mRNAs and process small stable RNAs then its not surprising that there is a variety of different RNA type molecules i. RNaseE in E.coli organizes the degradasome and catalyzes mRNA decay and 5sRNA maturation j. So you have your RNA binding domain, but in addition that is also a whole series of RNA hydrolytic or phosphorolytic enzymes so they can either use water to hydrolyze bonds w/in the RNA or they can use inorganic phosphate if it’s a phosphorolytic process i. But the degradosome isn’t just used for degradation, even though it is used for degradative purposes , its usually mRNA that are degraded, and the mRNA in E.coli has a very short half life ii. One of the elements that are always found in addition to the hydrolytic and phosphorolytic enzymes are Helicases 1. why would it be beneficial for a helicase to be associated w/ the degradasomes/exosomes? a. Because many of the RNAses don’t work on fully folded DNA/RNA, instead they require ssDNA/ssRNA, therefore have the helicases which will unfold the 2 dsDNA/dsRNA making it possible for the RNAses and RNA phosphorolytic enzymes to degrade the RNA
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b. But degradation is only 1 of the 2 fxns, there are lots of RNAs that are both in prokaryotes and eukaryotes like microRNA, miniRNAs, 5sRNA which is a component of the ribosomes, tRNA all of these fxn only if they’re processed i. That is the native gene when the DNA is transcribed into mRNA it is usually inactive and needs to be processed processing can involve hydrolysis of specific bonds w/in the molecule and they get further processed by methylation, or acetylation, or derivatization ii. In some cases particularly w/ the tRNA, there is a change of the nucleotides w/in the structure to alternative homologs 2. Carboxysomes: a. Fxn: To create a high [CO2] i. In the case of the cyanobacteria and their derived organelles itself, CO2, not bicarbonate is the molecule that is fixed
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Microbial Physiology notes lec20 11-12-10 - Microbial...

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